Mass spectrometric elucidation of the neuropeptidome of a crustacean neuroendocrine organ.

The blue crab Callinectes sapidus has been used as an experimental model organism for the study of regulation of cardiac activity and other physiological processes. Moreover, it is an economically and ecologically important crustacean species. However, there was no previous report on the characterization of its neuropeptidome. To fill in this gap, we employed multiple sample preparation methods including direct tissue profiling, crude tissue extraction and tissue extract fractionation by HPLC to obtain a complete description of the neuropeptidome of C. sapidus. Matrix-assisted laser desorption/ionization (MALDI)-Fourier transform mass spectrometry (FTMS) and MALDI-time-of-flight (TOF)/TOF were utilized initially to obtain a quick snapshot of the neuropeptide profile, and subsequently nanoflow liquid chromatography (nanoLC) coupled with electrospray ionization quadrupole time-of-flight (ESI-Q-TOF) tandem MS analysis of neuropeptide extracts was conducted for de novo sequencing. Simultaneously, the pericardial organ (PO) tissue extract was labeled by a novel N,N-dimethylated leucine (DiLeu) reagent, offering enhanced fragmentation efficiency of peptides. In total, 130 peptide sequences belonging to 11 known neuropeptide families including orcomyotropin, pyrokinin, allatostatin A (AST-A), allatostatin B (AST-B), FMRFamide-like peptides (FLPs), and orcokinin were identified. Among these 130 sequences, 44 are novel peptides and 86 are previously identified. Overall, our results lay the groundwork for future physiological studies of neuropeptides in C. sapidus and other crustaceans.